3
LLDP frame encapsulated in SNAP
Figure 3 SNAP-encapsulated LLDP frame
Table 2 Fields in a SNAP-encapsulated LLDP frame
Field Description
Destination MAC address
MAC address to which the LLDP frame is advertised. It is the same as that
for Ethernet II-encapsulated LLDP frames.
Source MAC address MAC address of the sending port.
Type
SNAP type for the upper-layer protocol. This field is
0xAAAA-0300-0000-88CC for LLDP.
Data LLDPDU.
FCS
Frame check sequence, a 32-bit CRC value used to determine the validity of
the received Ethernet frame.
LLDPDUs
Each LLDP frame contains one LLDPDU. Each LLDPDU is a sequence of type-length-value (TLV)
structures.
Figure 4 LLDPDU encapsulation format
As shown in Figure 4, each LLDPDU starts with the following mandatory TLVs: Chassis ID TLV, Port
ID TLV, and Time to Live TLV. The mandatory TLVs are followed by a maxiumu of 29 optional TLVs.
TLVs
A TLV is an information element that contains the type, length, and value fields.
LLDPDU TLVs include the following categories:
• Basic management TLVs.
• Organizationally (IEEE 802.1 and IEEE 802.3) specific TLVs.
• LLDP-MED (media endpoint discovery) TLVs.
Basic management TLVs are essential to device management.
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